Ball valves are widely used in various conditions for controlling the flow of mixtures. Such a mixture often includes small solid particles distributed in a fluid. In practice, in many mixtures, the solid particles are impurities. Alternatively, the mixture may be a media (e.g., a powder) and a (fluid) carrier therefor.
As is well known in the art, the ball may be held in place by valve seats, which are intended to permit the ball to move between open and closed positions. When the ball is in the open position, the mixture is permitted to flow through the ball. Often, the flow of the mixture through the ball is said to be from an upstream side to a downstream side, i.e., “upstream” and “downstream” typically refer to a direction of flow of the mixture through an open valve.
Controlling the flow of the mixture typically involves resisting pressure (i.e., a pressure differential) when the valve is closed. In practice, in many situations, when the ball is in the closed position, the mixture is subjected to pressure. Accordingly, when the ball is in the closed position, the valve is required to withstand pressure when the valve is closed. Such pressure may be directed in the downstream direction. Alternatively, such pressure may be directed in the upstream direction, depending on the circumstances.
In each ball valve, of necessity, gaps or apertures exist between the ball and the valve seats. Where (whether intentionally or otherwise) solid particles are included in the mixture controlled by the valve, the solid particles tend to accumulate in the gaps behind one or both of the valve seats (i.e., between the valve seats and the ball). In the prior art, the solid particles ultimately accumulate to the extent that the ball cannot be moved, at which point the valve is no longer functional.
Also, biasing means may be included in the prior art ball valve assemblies, e.g., for urging a valve seat against the ball. Typically, where a biasing means (e.g., a Belleville spring) is used, gaps are defined between the biasing means and the valve seat with which the biasing means is engaged, and solid particles tend to accumulate between the biasing means and the valve seat. Ultimately, sufficient particles accumulate to interfere with the biasing means' pressure on the valve seat.
Various attempts have been made in the prior art to address the problem of solid particles getting into the gaps between the valve seats and the ball. In general, these attempts usually involve seals intended to prevent the solid particles from getting into the gaps between the ball and the valve seats. Typically, the seals are positioned on the outer edges (i.e., between the valve seats' outer edges and the body) and on the inner side (i.e., the sides engaging the ball) of the valve seats respectively. However, these attempts to address the problem have some disadvantages. Since the seals must be dynamic (i.e., any such seal must accommodate the movement of the ball relative to the seal), any such seal eventually allows the solid particles to get into the gaps. In general, the seals tend to loosen somewhat with longer service. Also, once solid particles get between the ball and the seats, they tend to be trapped there by the seals. In this way, seals may exacerbate the problem.